Data transmission through wire-line multiple channels usually suffers from crosstalk interferences, such as echo, near-end crosstalk (NEXT), and far-end crosstalk (FEXT). Generally, FEXT is much smaller than echo and NEXT, and it can be tolerated. However, for high/ultra-high speed applications, such as 10 Gigabit Ethernet over copper (10GBASE-T), far-end crosstalk (FEXT) becomes one of the major impairments, which limit the quality and capacity of data transmission over unshielded twisted-pair (UTP) cable channels. To meet the desired throughput (10 Gbps) and target BER (10−12) requirements, novel FEXT cancellation schemes are needed in a multi-channel transceiver design.
Conventional technology that addresses FEXT interference is mainly based on the concept of noise cancellation. The FEXT canceller is employed at the receiver side to suppress FEXT interference. Due to the fact that the disturbing source of FEXT is generally unknown to the victims, it is difficult to apply an accurate input to the FEXT canceller at the receiver side. One prior technique made use of the tentative decision of the disturbing far-end transmit signal as the input to the FEXT canceller, and both the FEXT canceller and linear equalizer were jointly adapted to combat intersymbol interference (ISI) and FEXT (See, e.g., Gi-Hong Im, Kyu-Min Kang and Cheol-Jin Park, “FEXT Cancellation for Twisted-Pair Transmission,” IEEE J. Select. Areas Commun., vol. 20, no. 5, pp. 959-972, June 2002). However, the particular drawback of this technique is that the tentative decisions are only estimates of disturbing far-end transmit symbols, and incorrect tentative decisions occur in practice, which thereby increases the error rates. Instead of using the tentative decisions, another technique applied the actual decisions of the far-end transmit symbols to the input of the FEXT canceller, and a structure based on multi-input multi-output (MIMO) decision feedback was proposed to remove the FEXT crosstalk in digital subscriber line (DSL) systems (See, e.g., G. Ginis and J. Cioffi, “vectored transmission for digital subscriber line systems,” IEEE J. Select. Areas Commun., vol. 20, no. 5, pp. 1085-1104, June 2002). However, nonlinear feedback loops inside of this structure limit its use for high speed applications, and also the error propagation problem inherent in DFE structure remains unsolved. In real applications, it is found that FEXT exhibits non-causal characteristic which makes FEXT cancellation more difficult. In addition, the strength of FEXT varies significantly with different cables and connectors. For example, the effect of FEXT is dominant when cable length is between 20 and 50 meters. It is important to satisfy the performance of these transceivers at all lengths. In other words, a flexible solution needs to be developed to work under different cabling environments.
What is needed is a new design methodology and an implementation method for efficiently dealing with FEXT crosstalk that can overcome the limitation of the traditional schemes, achieve a better cancellation performance, and also be suitable for high speed VLSI implementation.